Communications device, infrastructure equipment, mobile communications network and methods

ABSTRACT

A communications device configured to transmit signals representing data to a first in-coverage communications device acting as source relay node for the communications device, the first in-coverage communications device configured to transmit signals to the infrastructure equipment of the mobile communications network, and to receive signals representing the data from the first in-coverage communications device acting as the source relay node. The source relay node is within a coverage area of the infrastructure equipment of the mobile communications network, the source relay node being configured to transmit the signals representing the data received from the communications device to the infrastructure equipment and to transmit the signals representing the data to the communications device which are received from the infrastructure equipment.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. application Ser. No.15/548,433, filed Aug. 3, 2017, which is based on PCT filingPCT/EP2016/052283 filed on Feb. 3, 2016, and claims priority to EuropeanPatent Application 15154659.5, filed in the European Patent Office on 11Feb. 2015, the entire contents of each of which being incorporatedherein by reference.

BACKGROUND Field of Disclosure Technical Field of the Disclosure

The present disclosure relates to communications devices and methods forcommunicating data using communications devices, and in particular tocommunications devices which are configured to perform device-to-devicecommunications.

BACKGROUND OF THE DISCLOSURE

Mobile telecommunication systems, such as those based on the 3GPPdefined UMTS and Long Term Evolution (LTE) architecture, are able tosupport more sophisticated services than simple voice and messagingservices offered by previous generations of mobile telecommunicationsystems. For example, with the improved radio interface and enhanceddata rates provided by LTE systems, a user is able to enjoy high datarate applications such as video streaming and video conferencing onmobile communications devices that would previously only have beenavailable via a fixed line data connection. The demand to deploy fourthgeneration networks is therefore strong and the coverage area of thesenetworks, i.e. geographic locations where access to the networks ispossible, is expected to increase rapidly. However, although thecoverage and capacity of fourth generation networks is expected tosignificantly exceed those of previous generations of communicationsnetworks, there are still limitations on network capacity and thegeographical areas that can be served by such networks. Theselimitations may, for example, be particularly relevant in situations inwhich networks are experiencing high load and high-data ratecommunications between communications devices, or when communicationsbetween communications devices are required but the communicationsdevices may not be within the coverage area of a network. In order toaddress these limitations, in LTE release-12 the ability for LTEcommunications devices to perform device-to-device (D2D) communicationswill be introduced. D2D communications allow communications devices thatare in close proximity to directly communicate with each other, bothwhen within and when outside of a coverage area or when the networkfails. This D2D communications ability can allow user data to be moreefficiently communicated between communications devices by obviating theneed for user data to be relayed by a network entity such as a basestation, and also allows communications devices that are in closeproximity to communicate with one another although they may not bewithin the coverage area of a network. The ability for communicationsdevices to operate both inside and outside of coverage areas makes LTEsystems that incorporate D2D capabilities well suited to applicationssuch as public safety communications, for example. Public safetycommunications require a high degree of robustness whereby devices cancontinue to communicate with one another in congested networks and whenoutside a coverage area. Whilst D2D communications techniques canprovide an arrangement for communicating between devices when thecommunications devices are outside a coverage area provided by mobilecommunications network, the D2D communications techniques can alsoprovide an arrangement for extending an coverage area of the mobilecommunications network, when one of the communications devices is withinthe coverage area and another is outside the coverage area.

SUMMARY OF THE DISCLOSURE

According to a first example embodiment of the present technique thereis provided a communications device configured to transmit signals toone or more other communications devices via a wireless access interfaceto perform device-to-device communications and to transmit signals viathe wireless access interface to an infrastructure equipment of a mobilecommunications network when within a radio coverage area of theinfrastructure equipment. The communications device includes a receiverconfigured to receive signals from the one or more other communicationsdevices via the wireless access interface and to receive signals via thewireless access interface from the infrastructure equipment of themobile communications network when within the radio coverage area of theinfrastructure equipment. A controller is configured with thetransmitter and the receiver to transmit signals representing the datato a first in-coverage communications device acting as source relay nodefor the communications device, the first in-coverage communicationsdevice being able to transmit signals to the infrastructure equipment ofthe mobile communications network, and to receive signals representingthe data from the first in-coverage communications device acting as thesource relay node. The source relay node is within a coverage area ofthe infrastructure equipment of the mobile communications network, thesource relay node being configured to transmit the signals representingthe data received from the communications device to the infrastructureequipment and to transmit the signals representing the data to thecommunications device which are received from the infrastructureequipment. Subject to predetermined conditions, the controller isconfigured to receive one or more beacon signals from one or more otherin-coverage communications devices which can act as a relay node for thecommunications device when out-of-coverage so that the receiver cannotreceive the signals from the infrastructure equipment or transmit thesignals to the infrastructure equipment, or to transmit a beacon signalto the one or more other in-coverage communications devices which canact as a relay node for the communications device when out-of-coverage,and to transmit the signals representing the data to one of the otherin-coverage communications devices to act as a target relay node fortransmitting the data to the infrastructure equipment, or to receive thesignals representing the data from one of the other in-coveragecommunications devices acting as a target relay node which have beenreceived from the infrastructure equipment.

Embodiments of the present technique can provide an arrangement inwhich, an out-of-coverage communications device, which is using anin-coverage communications device to act as a relay node to communicatedata to and/or from an infrastructure equipment can change affiliationfrom one in-coverage communications device to another.

Various further aspects and features of the present disclosure aredefined in the appended claims and include a communications device, amethod of communicating using a communications device.

BRIEF DESCRIPTION OF DRAWINGS

Embodiments of the present disclosure will now be described by way ofexample only with reference to the accompanying drawings wherein likeparts are provided with corresponding reference numerals and in which:

FIG. 1 provides a schematic diagram of a mobile communications system inwhich in coverage communications devices are communicating via aninfrastructure equipment and at least one out-of-coverage communicationsdevice is communicating via one of the in-coverage communicationsdevices;

FIG. 2 provides a schematic diagram of the structure of a downlink of awireless access interface of a mobile communications system;

FIG. 3 provides a schematic diagram of an uplink of a wireless accessinterface of a mobile communications system;

FIG. 4 provides a schematic diagram of an out-of-coverage communicationsdevice communicating on an uplink and a downlink with an infrastructureequipment via an in-coverage communications device;

FIG. 5 provides a schematic block diagram illustrating an arrangement inwhich a plurality of communications devices form a group which performdevice-to-device communications;

FIG. 6 is an illustrative representation of a message exchange flowdiagram for an intra-Mobility Management Entity (MME)/Serving Gatewayhandover process according to an conventional arrangement of an LTEstandard;

FIG. 7 is a schematic representation of part of an example process inwhich an out-of-coverage communications device changes an affiliationfor communicating data to an infrastructure equipment from onein-coverage communications device acting as a source relay node toanother in-coverage communications device acting as a target rely node;

FIG. 8 is a further part of the example process of FIG. 7;

FIG. 9 is a further part of the example process of FIG. 7;

FIG. 10 is a schematic representation of an alternative process to theexample process shown in FIG. 7;

FIG. 11 is a schematic representation of a further part of thealternative process shown in FIG. 10;

FIG. 12 is a schematic representation of part of another example processin which an out-of-coverage communications device changes an affiliationfor communicating data to an infrastructure equipment from onein-coverage communications device acting as a source relay node toanother in-coverage communications device acting as a target rely node;and

FIG. 13 is a further part of the example process shown in FIG. 12.

DESCRIPTION OF EXAMPLE EMBODIMENTS Conventional Communications System

FIG. 1 provides a schematic diagram illustrating some basicfunctionality of a mobile telecommunications network/system 100operating in accordance with LTE principles and which may be adapted toimplement embodiments of the disclosure as described further below.Various elements of FIG. 1 and their respective modes of operation arewell-known and defined in the relevant standards administered by the3GPP (RTM) body, and also described in many books on the subject, forexample, Holma H. and Toskala A [1]. It will be appreciated thatoperational aspects of the telecommunications network which are notspecifically described below may be implemented in accordance with anyknown techniques, for example according to the relevant standards.

FIG. 1 provides a schematic diagram of a conventional mobiletelecommunications system 100, where the system includes mobilecommunications devices 101, infrastructure equipment 102, and a corenetwork comprising a serving gateway node 103, a packet data gateway 104which forms a gateway to an external network 105. The infrastructureequipment 102 may also be referred to as a base station, networkelement, enhanced Node B (eNodeB) or a coordinating entity for example,and provides a wireless access interface to the one or morecommunications devices within a coverage area or cell. The one or moremobile communications devices may communicate data via the transmissionand reception of signals representing data using the wireless accessinterface. The infrastructure equipment 102 is communicatively linkedvia the serving gateway node 103 and the packet data gateway 104 to theexternal network 105, which may be connected to one or more othercommunications systems or networks which have a similar structure tothat formed from communications devices 101 and infrastructure equipment102. The core network may also provide functionality includingauthentication, mobility management, charging and so on for thecommunications devices served by the network entity.

The mobile communications devices of FIG. 1 may also be referred to ascommunications terminals, user equipment (UE), terminal devices and soforth, and are configured to communicate with one or more othercommunications devices served by the same or a different coverage areavia the network entity. These communications may be performed bytransmitting and receiving signals representing data using the wirelessaccess interface over the two way communications links represented bylines 106 to 111, where arrows 106, 108 and 110 represent downlinkcommunications from the network entity to the communications devices andarrows 107, 109 and 111 represent the uplink communications from thecommunications devices to the infrastructure equipment 102. Thecommunications system 100 may operate in accordance with any knownprotocol, for instance in some examples the system 100 may operate inaccordance with a 3GPP Long Term Evolution (LTE) standard where theinfrastructure equipment 102 may be referred to as a base station or anenhanced Node B (eNodeB(eNB)).

Also shown in FIG. 1 is a line 140 which represents an indication of amaximum range within which radio signals can be communicated to and fromthe infrastructure equipment or eNB 102. As will be appreciated the line140 is just an illustration and in practice there will be a greatvariation in respect of the propagation conditions and therefore therange in which radio signals can be communicated to and from the eNB102. As shown in FIG. 1, in one example one of the communicationsdevices 112 has moved to an area which is outside the line 140representing a range within which radio signals can be communicated toand from the eNB 102. According to the present technique thecommunications terminal 112 which is outside the range of the eNB 102may still communicate data to and from the eNB 102 but this is achievedby relaying the data via one of the UE's 114 which acts as a relay nodeto the communications terminal 112.

In accordance with our pending International patent applicationsnumbered PCT/2014/078087, PCT/2014/078093, PCT/2014/079338,PCT/2014/077447, PCT/2014/077396, PCT/2014/079335, the contents of whichis incorporated herein by reference, there is provided a devicecommunications technique which allows one or more communications devicesto form a group of communications devices which can communicate databetween the group of communications devices without being communicatedvia an eNB. Such an arrangement can operate within or without a coveragearea provided by a base station or eNB.

In one example 3GPP have completed a study item entitled “LTE Device toDevice Proximity Services-Radio Aspects” described in a technical reportTR36.843. According to the present technique therefore an arrangement isprovided in which a UE 112 which falls outside a coverage area of an eNB102 is able to communicate to the eNB 103 using one of the UEs which iswithin coverage by acting as a relay node. To this end, UEs 112, 114perform device-to-device (D2D) communications. However, a technicalproblem addressed by the present technique concerns an arrangement inwhich an out-of-coverage UE 112 performs a handover to anotherin-coverage UE 114 which is to act as a relay node.

In a situation in which an out-of-coverage UE is communicating with amobile communications network via an in-coverage UE acting as a relaynode, there are several mobility scenarios which can be considered.After an initial relay selection by an out-of-coverage UE there needs tobe a way to select and connect from a source relay UE to a target relayUE. Such an intra relay UE handover or re-selection requires anarrangement in which an out-of-coverage UE discovers the target relayUE. However, since an in-coverage UE acting as a relay node may notalways be transmitting a downlink signal, for example a discovery beaconsignal, then it may not be possible to make a comparison of measurementsfrom the current or source relay UE node (relay or eNB) and a potentialtarget relay node (relay). This differs from the typical handover from asource eNB to a target eNB, because the eNB always transmits downlinkcommon channels and synchronisation channels, so that the UE can alwaysperform the measurement.

Accordingly a technical problem addressed by the present techniqueconcerns an arrangement in which an out-of-coverage UE changes from onein-coverage UE acting as a relay node to another in-coverage UE actingas a relay. In the following description these will be referred to as asource relay-UE and a target relay-UE.

LTE Wireless Access Interface

A brief description of the LTE wireless access interface is explained inthe following paragraphs with reference to FIGS. 2 and 3 to support theexplanation of the example embodiments of the present technique whichare provided in the following paragraphs.

Mobile telecommunications systems such as those arranged in accordancewith the 3GPP defined Long Term Evolution (LTE) architecture use anorthogonal frequency division modulation (OFDM) based wireless accessinterface for the radio downlink (so-called OFDMA) and a single carrierfrequency division multiple access scheme (SC-FDMA) on the radio uplink.In accordance with the present technique, the wireless access interfacefor both the down-link shown in FIG. 2 and the up-link shown in FIG. 3can provide a facility for communicating data from a UE to a mobilecommunications network via the eNB and for communicating data to the UEfrom the eNB, but can also provide communications resources forperforming D2D communications to another communications device withoutbeing communicated via the eNB. The down-link and the up-link of thewireless access interface of FIGS. 2 and 3 respectively will now beexplained.

FIG. 2 provides a simplified schematic diagram of the structure of adownlink of a wireless access interface that may be provided by or inassociation with the eNodeB of FIG. 1 when the communications system isoperating in accordance with the LTE standard. In LTE systems thewireless access interface of the downlink from an eNodeB to a UE isbased upon an orthogonal frequency division multiplexing (OFDM) accessradio interface. In an OFDM interface the resources of the availablebandwidth are divided in frequency into a plurality of orthogonalsubcarriers and data is transmitted in parallel on a plurality oforthogonal subcarriers, where bandwidths between 1.25 MHZ and 20 MHzbandwidth may be divided into 128 to 2048 orthogonal subcarriers forexample. Each subcarrier bandwidth may take any value but in LTE it isfixed at 15 KHz. As shown in FIG. 2, the resources of the wirelessaccess interface are also temporally divided into frames where a frame200 lasts 10 ms and is subdivided into 10 subframes 201 each with aduration of 1 ms. Each subframe is formed from 14 OFDM symbols and isdivided into two slots each of which comprise six or seven OFDM symbolsdepending on whether a normal or extended cyclic prefix is beingutilised between OFDM symbols for the reduction of inter symbolinterference. The resources within a slot may be divided into resourcesblocks 203 each comprising 12 subcarriers for the duration of one slotand the resources blocks further divided into resource elements 204which span one subcarrier for one OFDM symbol, where each rectangle 204represents a resource element. More details of the down-link structureof the LTE wireless access interface are provided in Annex 1.

FIG. 3 provides a simplified schematic diagram of the structure of anuplink of an LTE wireless access interface that may be provided by or inassociation with the eNodeB of FIG. 1. In LTE networks the uplinkwireless access interface is based upon a single carrier frequencydivision multiplexing FDM (SC-FDM) interface and downlink and uplinkwireless access interfaces may be provided by frequency divisionduplexing (FDD) or time division duplexing (TDD), where in TDDimplementations subframes switch between uplink and downlink subframesin accordance with predefined patterns. However, regardless of the formof duplexing used, a common uplink frame structure is utilised. Thesimplified structure of FIG. 3 illustrates such an uplink frame in anFDD implementation. A frame 300 is divided in to 10 subframes 301 of 1ms duration where each subframe 301 comprises two slots 302 of 0.5 msduration. Each slot is then formed from seven OFDM symbols 303 where acyclic prefix 304 is inserted between each symbol in a manner equivalentto that in downlink subframes. More details of the LTE up-linkrepresented in FIG. 3 are provided in Annex 1.

Supporting an Out-of-Coverage Communications Device

It has previously been proposed to provide some arrangement for deviceto device communication within standards which define communicationssystems according to specifications administered by the 3GPP referred toas Long Term Evolution (LTE). These are defined in LTE Release 12 andRelease 13 and provide a facility for D2D communications. Moregenerally, a number of possible approaches to the implementation of LTED2D communications exist. For example, the wireless access interfaceprovided for communications between UEs and eNodeB may be used for D2Dcommunications, where an eNB allocates the required resources andcontrol signalling is communicated via the eNB but user data istransmitted directly between UEs.

In our co-pending International patent applications with the applicationnumbers PCT/2014/078087, PCT/2014/078093, PCT/2014/079338,PCT/2014/077447, PCT/2014/077396, PCT/2014/079335, there is disclosedvarious techniques for performing D2D communications between devicesusing the LTE up-link shown in FIG. 3. For example, in the Internationalpatent application PCT/2014/079338, there is disclosed an arrangementfor performing contentious resolution for D2D communications. Similarly,an arrangement for allocating resources using a scheduling assignmentmessages transmitted in a scheduling assignment region of an uplinktransmission frame is disclosed in International patent applicationPCT/2014/078093. An arrangement in which communications devices oflimited capability which may form machine to machine communicationsdevices can be arranged to perform device to device communicationswithin a limited set of resources (referred to as a virtual carrier) asdisclosed in International patent application PCT/2014/077447.Furthermore, an arrangement for identifying resources which can be usedfor device to device communications between a group of communicationsdevices is disclosed in International patent applicationPCT/2014/079335, the content of all of the above International patentapplications are incorporated into the present application by reference.As will be appreciated therefore these co-pending international patentapplications disclose an arrangement for an out-of-coverage UE 112 tocommunicate on a forward or up-link to an in-coverage UE acting as arelay node 114, represented by an arrow 120 in FIG. 1 and to communicateon a reverse or down-link from the relay-UE 114 to the out-of-coverageUE 112 as represented by an arrow 122 in FIG. 1.

FIG. 4 shows a schematic block diagram of a communications path betweenthe out of coverage UE 112 and the eNB 102, via the in coverage UEacting as a relay node 114. As shown in FIG. 4 the out of coverage UE112 includes a transmitter 401 a receiver 402 and a controller 404 tocontrol the transmission and reception of signals to the in coverage UE114 acting as a relay node. The up-link signals are represented by anarrow 120 which corresponds to that shown in FIG. 1 and the downlinksignals are shown by an arrow 122, which corresponds to that shown inFIG. 1. The relay UE 114 could be a conventional UE and so includes alsoa transmitter 401 receiver 402 and a controller 404. The in coverage UEacting as a relay node 114 operates in accordance with a conventionalarrangement but transmits signals on the uplink as shown by an arrow 107and receives signals on the downlink as represented by an arrow 106 toand received from the eNB 102 respectively. The eNB 102 includes atransmitter 404 a receiver 408 and a controller 410 which may include ascheduler for scheduling the transmission and reception of signals onthe downlink and the uplink in accordance with the wireless accessinterface shown in FIGS. 2 and 3.

As explained above, embodiments of the present technique can provide anarrangement for extending the coverage of an eNB, by utilising D2Dcommunications techniques. An example application is presented in FIG.5. In FIG. 5, a plurality of communications devices 501, 502, 504, 114form a group of communications devices 604 for which D2D communicationsis desired for the reasons explained above. As represented in FIG. 5,the communications devices 501, 502, 504, are outside a coverage arearepresented by a line 601 of an eNB or base station 602. As such the eNB602 cannot form or control any of the communications between the out ofcoverage communications devices 501, 502, 504. According to the presenttechnique a plurality of communications devices 604 may perform D2Dcommunications whether they are in coverage or out of coverage of an eNB102. As shown in FIG. 5 the group of devices 604 includes UEs 501, 502,504, which are out of coverage of the eNB 602 with one of the UEs 114within coverage. To this end, an in coverage UE 114 is operating to actas a relay node. Accordingly, in one example, the out of coverage UEs501, 502, 504 may form a virtual cell with the relay node or in coverageUE 114 acting as a base station for each of these out of coverage UEs501, 502, 504. Accordingly, a broken or dash line 510 illustrates acoverage area of a virtual cell formed by the in coverage UE 114. In oneexample, all control plane signalling is communicated to the eNB 102 viathe in coverage UE 114 acting as a relay node so that the control planeis managed by the virtual cell.

As explained above, embodiments of the present technique can provide anarrangement in which an out-of-coverage UE, which is communicating viaone source and in-coverage UE acting as a relay UE can identify anothertarget in-coverage UE to act as a relay node in place of the sourcerelay UE, when the source relay UE can no longer act as a relay nodebecause the communications link with that source relay UE is no longerviable. Accordingly embodiments of the present technique can provided anarrangement in which an out-of-coverage UE can change affiliation thatis perform a hand over from one in coverage UE acting as a relay node toanother. Conventionally UE's perform measurements of beacon signalstransmitted by base stations of eNBs in order to determine which eNBprovides a better link quality where a beacon signal received from acurrently used base station falls below a pre-determined level.Embodiments of the present technique can provide in one example:

-   -   Measurements of a received signal are made by or reported to the        current or source relay UE.    -   The source relay UE then will trigger potential target relays to        transmit a handover discovery beacon, either directly or via the        eNB.    -   The out-of-coverage UE then performs measurements of potential        target relay UE and reports the results to the source relay UE.    -   Handover to a target relay is then triggered based on the        reported measurements.    -   Alternatively no measurements are reported, and the        out-of-coverage UE performs a target relay UE reselection        autonomously.

According to an alternative arrangement embodiments of the presenttechnique can provide:

-   -   Measurements are made by the out-of-coverage UE of a beacon        signal transmitted from a current or source relay UE.    -   The out-of-coverage UE triggers a beacon signal transmission        when measurements are below a threshold.    -   In-coverage UEs which can act as potential target relay UEs and        the current source relay UE monitor for the beacon signal        transmitted by the out-of-coverage UE. All of the in-coverage        UE, which can act as a relay UE can perform measurements of the        out-of-coverage UE beacon signal and report the results to the        eNB.    -   Handover to a target relay UE is then triggered based on the        reported measurements of the beacon signal from the        out-of-coverage UE measured by the in-coverage UEs which can act        as a new or target UE.    -   A handover command may be sent by the source relay UE, or        another approach could be to send a “PULL” message from the        target relay UE, which is almost like a reselection but with the        initial access message coming from the network relay side        instead of the out-of-coverage UE.

Intra-MME/Serving Gateway Handover

In order to provide a better appreciation of example embodiments of thepresent technique a brief description of a conventional handovertechnique by a UE from a source eNB 606 to a target eNB 608 is providedin the following paragraphs with reference to FIG. 6. FIG. 6 presents amessage flow diagram of a current handover procedure for LTE betweeneNBs 606, 608. As shown in FIG. 6 a UE 605 first receives a measurementcontrol message M1 and then performs packet data transmissions to andfrom the UE 605 shown by an operation S1. In an uplink allocationmessage the source eNB 606 transmits an allocation of resources to theUE 605. The UE 605 after performing measurements transmits a measurementreport message to the source eNB 606. In a process step 612 the UEdetermines whether or not to handover to a target base station in thiscase the target eNB 608. The source eNB 606 then transmits a handoverrequest message in a message M4 and the target eNB 608 performs anadmission control step S5. The target eNB 608 transmits a handoverrequest acknowledgement M6 to the source eNB 606 which then transmits adownlink allocation message 614 to the UE 605. An RRC collectionre-confirmation and mobility control information is then transmitted bythe source eNB 606 to the UE 605 in preparation former handover in amessage M7. In steps 616, 618 and the UE 605 detaches from the old celland synchronises with the new cell and buffers data for transmission viathe target eNB. In the message M8 the source eNB 606 transmits a statustransfer and follows by data forwarding in a transmission step 620. Thetarget eNB 608 then buffers packets from the source eNB 608 for thedownlink transmission 622 under instruction from the MME 624. The UEthen transmits a synchronisation message M9 and receives an uplinkallocation of resources the message M10 which is acknowledged by an RRCconnection confirmation repeat message M11. In process steps S3 the eNBtransmits data packets to and from the target eNB to the servinggateway. The target eNB 608 then transmits a path switch request to theMME 624 which transmits a modified bearer request to the serving gateway630 in a message M13. In a step S14 the serving gateway then switchesthe downlink path which is transmitted to the source eNB 601 in amessage S4. The source eNB then transmits an end marker message to thetarget eNB 602 in a step S6 and the data packets are transmitted fromthe target eNB to the serving gateway S8. The serving gateway 630 thentransmits a modifying bearer request message M15 to the MME 624 whichthen transmits a path switch request acknowledgement message M16 to thetarget eNB 608 and the target eNB 608 transmits a UE context releasemessage M17 to the source eNB 606. The source eNB 606 then performs arelease resources process in step S10.

As will be appreciated from the flow diagram shown in FIG. 6 now severalsteps and processes which are conventionally formed in connection with ahandover from a source eNB 606 to the target eNB 608. A technicalproblem is then presented because a UE which is constructed to operateand communicate via the wireless access interface shown in FIGS. 2 and 3must be adapted to perform a handover process from one relay node toanother. Furthermore, the relay nodes may themselves be fluctuatingbecause they maybe mobile so that the group of UEs which areout-of-coverage and in coverage maybe dynamically changing as these UEsmove around. Therefore according to the present technique, handoverbetween relay UEs should follow a similar procedure, to that shown inFIG. 6, with the main two differences being that the D2DSS needs to betriggered so that the UE can perform measurements (before step 1 above)and the signalling between the UE and the eNB needs to be relayed, sothat a source and a target are relay UEs, each controlled by a host eNB.

The present technique therefore provides an arrangement which allows anout-of-coverage UE 112 to select a different in-coverage UE to act as arelay node in accordance with a best available communications path toand from that UE. In one example, as represented in FIGS. 7, 8, 9, 10and 11, the current in coverage UE acting as a relay node operates thetrigger potential targets to act as relay nodes to transmit a handoverdiscovery beacon which can be detected by the UE. As a second example asshown in FIGS. 10, 11 and 12 the out of coverage UE itself triggers abeacon signal transmission when measurements of the current source relayUE fall below a pre-determined threshold. These embodiments will now beexplained in the following sections:

Triggering of Relay D2DSS for Handover Measurements

FIG. 7 provides an example illustration of an embodiment of the presenttechnique, which is applicable to a handover between a source and targetrelay UE, for the Rel-13 UE-network directed relay case.

In step 1, the UE sends a device to device synchronisation signal(D2DSS) and data to an in-coverage UE 114 acting as a relay node (relayUE). In step 2 the relay UE 114 performs measurements of the receivedD2DSS, such as a received signal strength indication. In one example therelay UE 114 may send the D2DSS, and the out of coverage UE 112 performsmeasurements of the D2DSS transmitted by the relay UE 114, and thenreports any measurements such as the received signal strength indicationto the relay UE 114 along with data being transmitted. In accordancewith the present technique, an arrangement is therefore provided toensure that the radio quality is measured on the link between theout-of-coverage UE 112 and the relay UE 114.

In step 3 the relay UE 114 will then report the measurement back to theeNB 102. According to the above explanation steps 1, 2 and 3 arecompatible with a conventional LTE operation in that the UE firstperforms measurements on the current serving cell, and reports back whenthe received signal strength of the measure signal such as the beaconsignal goes below a threshold. This may then trigger step 1 in FIG. 7.Other alternative steps include performing intra-frequency orinter-frequency measurements during step 1, and reporting event A3, inaccordance with a conventional arrangement for example. The level ofreported neighbour cells and frequencies may be taken into account whenmaking the decision whether to activate relays (for example, relays areactivated only when there are no suitable eNB neighbour reported forhandover). However inter-frequency measurements may be enabled based onevent A2.

As shown in FIG. 8, in step 4 the eNB 102 commands potential in coverageUEs acting as relay nodes to start sending a D2DSS, for example usingRRC signalling. In step 5 the UE may then receive a measurement commandfrom the source relay UE 114 to start measurements. In one example,measurements may have been started automatically, which would involveless signalling overhead and delay. The out-of coverage UE 112 may beprovided with an “active set” and “monitored set” of relays formed fromin-coverage UEs for example. In step 6 the out-of-converge UE 112reports measurement results back to the source relay UE 114. In oneexample the reporting back to the relay UE 114 may be event triggered,such as upon detecting that another relay has become better than thesource relay UE, or it may be a one-shot or periodic measurement). RelayUEs are identified for example by using the D2DSS index, an identifier,or code which uniquely identifies the relay within the cell (eNB).

As shown in FIG. 9, in step 7 the measurement report, which has beenreceived by the source relay UE 114 is communicated back to the eNB 102either by relaying the measurement report message from theout-of-coverage UE 112 directly, or by simply indicating the newlyidentified target relay UE. This later example indicates that the sourcerelay UE 114 or the out-of-coverage UE 112 has already selected thetarget relay UE. Step 8 configures the target relay UE to be prepared toconnect to the out-of-coverage UE 112, and provides the source relay UE114 with the handover command.

At step 10 the UE has selected the new relay UE 900 (as target relay UE)and the procedure is complete. In one example the out-of-coverage UE 112may provide the new relay UE 900 with a “handover complete” messagesimilar to inter-eNB handover.

As an alternative example, step 8 may be done (more efficiently) inadvance as part of step 4, in order to reduce signalling and delay. Thatis to say that a potential target relay UE 114 may in one exampleembodiment be arranged to prepare to act as a new relay UE 900 beforebeing instructed to transmit the D2DSS. If this is the case then themeasurement report in step 7 does not need to be sent to the eNB butrather the handover command in step 9 is sent by the source relay UE 114in response to the measurement report in step 6. This examplearrangement is illustrated by the diagram shown in FIGS. 10 and 11.

As can be understood from FIGS. 10 and 11, the transmission of the relayD2DSS for handover measurements is triggered with for handoverpreparation in advance. As can be seen in FIG. 10, the out-of-coverageUE 112 in step 1 detects that the received signal strength (RSRP) hasfallen below a predetermined threshold, which then triggers ameasurement report in step 2 to the source relay-UE 114, which isreported to the eNB 102 in step 3. The preparation for handover inadvance provides a more efficient method of changing the relay node fromsource 114 to target 900, by reducing signalling with the eNB 102 andalso delay. As shown in FIG. 11, in one example there could be anautomatic switch from the source relay-UE 114 to the target relay UE900, which is similar to cell reselection, rather than to perform step6, which is similar to handover. This may further reduce the delay, andsince all of the target relay UEs are prepared to connect to the UE,this automatic selection of the new relay-UE 900 is possible. Thetransfer of any core network context information would then be dealtwith entirely by the eNB in combination with other network entities. Thenew relay-UE 900 would in effect treat this as a newly connecting UE.However in some examples an initial phase of establishing the contextinformation may be different due to prior knowledge of theout-of-coverage UE 112 having been provided by the eNB 102. Once theout-of-coverage UE 112 selects a new relay UE 900 and provides anindication to the new relay UE 900, the eNB 102 can transfer the contextbased on knowledge of the source relay-UE 114 within the eNB 102 andcore network. In summary the two approaches identified above are:

-   -   cell automatic reselection type arrangement in which an        out-of-coverage UE automatically selects a new relay-UE in        accordance with a received signal strength of the D2DSS, without        instruction from the eNB, or    -   handover procedure in which the eNB directs the UE to handover        to a target relay-UE.

Each of these options provides different advantages. For example,although the cell reselection procedure may provide an approach withless signalling overhead, it may be preferable to use the handover-likeprocedure in order to establish appropriate context information.

Transmission by Out-of-Coverage UE of D2DSS for Handover Measurements

According to another embodiment of the present technique there isprovided an arrangement in which an out-of-coverage UE 112 transmits abeacon signal, in preparation for a change of relay-UE from anin-coverage UE 114, rather than the beacon signal (D2DSS) beingtransmitted by the candidate relay UEs. According to this example anadvantage is provided in potentially reducing a delay and an amount ofsignalling message between the source relay UE 114 and out-of-coverageUE 112. The communication of the signalling messages may be on apotentially poor radio link. However the reduction in delay andsignalling messages transmitted on a potentially poor radio link may beat the expense of increased signalling messages, which are required tobe transmitted between any potential relays 101, 900 and the eNB 102,which are the measurement reports. This example embodiment may be morerobust since the additional signalling would be performed only by relayUEs 101, 900 in coverage of an eNB 102, which may be less error pronethan sending measurement reports via a source relay UE 114 with respectto which the out-of-coverage UE 112 is moving away from. Only the relayUEs 101, 900, which are measuring a good signal strength of the beaconsignal (D2DSS) transmitted from the out-of-coverage UE 112 need to bereported. Therefore a signalling overhead can be reduced. Thereselection-type approach would not be possible, however it might bepossible for a target relay to connect to the UE after UE losescommunication with the source relay.

FIGS. 12 and 13 provide an illustrative embodiment of the presenttechnique. As shown in FIG. 12 as a first step 1, the out-of-coverage UE112 detects that a received signal strength of a reference power hasfallen below a predetermined threshold, which therefore triggers aprocess in which the out-of-coverage UE 112 begins to select a new relayUE. In contrast to the example embodiment explained above with referenceto FIGS. 7 to 11, the out-of-coverage UE 112 then transmits a beaconsignal in step 2 to each of the in coverage UEs 604 which could act asrelay node. In step 3, the measured reference signal received power(RSRP) representing a signal strength of the beacon signal received fromthe out-of-coverage UE 112 is reported by each of the availablein-coverage UEs to the eNB 102. The eNB then compares the results fromeach of the in-coverage UEs and selects one of these to be the targetrelay-UE 900.

As shown in FIG. 13, in step 4, the eNB 102, having determined which ofthe in-coverage UEs should act as a relay-UE 900, transmits a handovercommand to the target relay UE 900. In accordance with process step 4,the handover command is sent via the target relay UE 900, rather thanthe source relay-UE 114, in order to address a potential loss ofcoverage from the source relay UE 114. Accordingly, this process woulddiffer from a conventional handover command because the out-of-coverageUE 112 can receive the handover command in communications resources ofthe down-link which are already known. For example the same down-linkcommunications resources that were configured for the source relay UE114, can be used for the target relay UE 900 using something like a“PULL” message to complete the relay change/handover. According to thisexample embodiment, a reduction in an amount of D2D communicationsresources which may be required for beacon signal transmission may beachieved, because only the out-of-coverage UE 112 transmits a beaconsignal rather than multiple in-coverage UEs which can act as relaynodes. Furthermore a reduction in amount of signalling messages may beachieved on D2D communications.

Summary

From the above explanation it will be appreciated that embodiments ofthe present technique can provide:

-   -   Methods for switching on multiple target relay beacon signals        for use with measurement evaluation for handover/relay        reselection.    -   Relays do not need to continuously send the D2DSS/beacon, which        saves resources and battery in the relay.

Various further aspects and features of the present invention aredefined in the appended claims and various combinations of the featuresof the dependent claims may be made with those of the independent claimsother than the specific combinations recited for the claim dependency.Modifications may also be made to the embodiments hereinbefore describedwithout departing from the scope of the present invention. For instance,although a feature may appear to be described in connection withparticular embodiments, one skilled in the art would recognise thatvarious features of the described embodiments may be combined inaccordance with the disclosure.

Annex 1

The simplified structure of the downlink of an LTE wireless accessinterface presented in FIG. 2, also includes an illustration of eachsubframe 201, which comprises a control region 205 for the transmissionof control data, a data region 206 for the transmission of user data,reference signals 207 and synchronisation signals which are interspersedin the control and data regions in accordance with a predeterminedpattern. The control region 204 may contain a number of physicalchannels for the transmission of control data, such as a physicaldownlink control channel (PDCCH), a physical control format indicatorchannel (PCFICH) and a physical HARQ indicator channel (PHICH). The dataregion may contain a number of physical channel for the transmission ofdata, such as a physical downlink shared channel (PDSCH) and a physicalbroadcast channels (PBCH). Although these physical channels provide awide range of functionality to LTE systems, in terms of resourceallocation and the present disclosure PDCCH and PDSCH are most relevant.Further information on the structure and functioning of the physicalchannels of LTE systems can be found in [1].

Resources within the PDSCH may be allocated by an eNodeB to UEs beingserved by the eNodeB. For example, a number of resource blocks of thePDSCH may be allocated to a UE in order that it may receive data that ithas previously requested or data which is being pushed to it by theeNodeB, such as radio resource control (RRC) signalling. In FIG. 2, UE1has been allocated resources 208 of the data region 206, UE2 resources209 and UE resources 210. UEs in a an LTE system may be allocated afraction of the available resources of the PDSCH and therefore UEs arerequired to be informed of the location of their allocated resourceswithin the PDCSH so that only relevant data within the PDSCH is detectedand estimated. In order to inform the UEs of the location of theirallocated communications resources, resource control informationspecifying downlink resource allocations is conveyed across the PDCCH ina form termed downlink control information (DCI), where resourceallocations for a PDSCH are communicated in a preceding PDCCH instancein the same subframe. During a resource allocation procedure, UEs thusmonitor the PDCCH for DCI addressed to them and once such a DCI isdetected, receive the DCI and detect and estimate the data from therelevant part of the PDSCH.

Each uplink subframe tray include a plurality of different channels, forexample a physical uplink shared channel (PUSCH) 305, a physical uplinkcontrol channel (PUCCH) 306, and a physical random access channel(PRACH). The physical Uplink Control Channel (PUCCH) may carry controlinformation such as ACK/NACK to the eNodeB for downlink transmissions,scheduling request indicators (SRI) for UEs wishing to be scheduleduplink resources, and feedback of downlink channel state information(CSI) for example. The PUSCH may carry UE uplink data or some uplinkcontrol data. Resources of the PUSCH are granted via PDCCH, such a grantbeing typically triggered by communicating to the network the amount ofdata ready to be transmitted in a buffer at the UE. The PRACH may bescheduled in any of the resources of an uplink frame in accordance witha one of a plurality of PRACH patterns that may be signalled to UE indownlink signalling such as system information blocks. As well asphysical uplink channels, uplink subframes may also include referencesignals. For example, demodulation reference signals (DMRS) 307 andsounding reference signals (SRS) 308 may be present in an uplinksubframe where the DMRS occupy the fourth symbol of a slot in whichPUSCH is transmitted and are used for decoding of PUCCH and PUSCH data,and where SRS are used for uplink channel estimation at the eNodeB.Further information on the structure and functioning of the physicalchannels of LTE systems can be found in [1].

In an analogous manner to the resources of the PDSCH, resources of thePUSCH are required to be scheduled or granted by the serving eNodeB andthus if data is to be transmitted by a UE, resources of the PUSCH arerequired to be granted to the UE by the eNB. At a UE, PUSCH resourceallocation is achieved by the transmission of a scheduling request or abuffer status report to its serving eNodeB. The scheduling request maybe made, when there is insufficient uplink resource for the UE to send abuffer status report, via the transmission of Uplink Control Information(UCI) on the PUCCH when there is no existing PUSCH allocation for theUE, or by transmission directly on the PUSCH when there is an existingPUSCH allocation for the UE. In response to a scheduling request, theeNodeB is configured to allocate a portion of the PUSCH resource to therequesting UE sufficient for transferring a buffer status report andthen inform the UE of the buffer status report resource allocation via aDCI in the PDCCH. Once or if the UE has PUSCH resource adequate to senda buffer status report, the buffer status report is sent to the eNodeBand gives the eNodeB information regarding the amount of data in anuplink buffer or buffers at the UE. After receiving the buffer statusreport, the eNodeB can allocate a portion of the PUSCH resources to thesending UE in order to transmit some of its buffered uplink data andthen inform the UE of the resource allocation via a DCI in the PDCCH.For example, presuming a UE has a connection with the eNodeB, the UEwill first transmit a PUSCH resource request in the PUCCH in the form ofa UCI. The UE will then monitor the PDCCH for an appropriate DCI,extract the details of the PUSCH resource allocation, and transmituplink data, at first comprising a buffer status report, and/or latercomprising a portion of the buffered data, in the allocated resources.

Although similar in structure to downlink subframes, uplink subframeshave a different control structure to downlink subframes, in particularthe upper 309 and lower 310 subcarriers/frequencies/resource blocks ofan uplink subframe are reserved for control signaling rather than theinitial symbols of a downlink subframe. Furthermore, although theresource allocation procedure for the downlink and uplink are relativelysimilar, the actual structure of the resources that may be allocated mayvary due to the different characteristics of the OFDM and SC-FDMinterfaces that are used in the downlink and uplink respectively. InOFDM each subcarrier is individually modulated and therefore it is notnecessary that frequency/subcarrier allocation are contiguous however,in SC-FDM subcarriers are modulation in combination and therefore ifefficient use of the available resources are to be made contiguousfrequency allocations for each UE are preferable.

As a result of the above described wireless interface structure andoperation, one or more UEs may communicate data to one another via acoordinating eNodeB, thus forming a conventional cellulartelecommunications system. Although cellular communications system suchas those based on the previously released LTE standards have beencommercially successful, a number of disadvantages are associated withsuch centralised systems. For example, if two UEs which are in closeproximity wish to communicate with each other, uplink and downlinkresources sufficient to convey the data are required. Consequently, twoportions of the system's resources are being used to convey a singleportion of data. A second disadvantage is that an eNodeB is required ifUEs, even when in close proximity, wish to communicate with one another.These limitations may be problematic when the system is experiencinghigh load or eNodeB coverage is not available, for instance in remoteareas or when eNodeBs are not functioning correctly. Overcoming theselimitations may increase both the capacity and efficiency of LTEnetworks but also lead to the creations of new revenue possibilities forLTE network operators.

The following numbered paragraphs provide further example aspects andfeatures of the present technique:

Paragraph 1. A communications device, comprising

-   -   a transmitter configured to transmit signals to one or more        other communications devices via a wireless access interface to        perform device-to-device communications, the wireless access        interface being provided for transmitting signals to an        infrastructure equipment of a mobile communications network when        within a radio coverage area of the infrastructure equipment,    -   a receiver configured to receive signals from the one or more        other communications devices via the wireless access interface,        the wireless access interface being provided for receiving        signals from the infrastructure equipment of the mobile        communications network when within the radio coverage area of        the infrastructure equipment, and    -   a controller for controlling the transmitter and the receiver to        transmit or to receive the signals via the wireless access        interface to transmit or to receive data represented by the        signals, and subject to predetermined conditions, the controller        is configured is configured in combination with the transmitter        and the receiver    -   to receive one or more beacon signals from one or more other        in-coverage communications devices which can act as a relay node        for the communications device when out-of-coverage so that the        receiver cannot receive the signals from the infrastructure        equipment or transmit the signals to the infrastructure        equipment, or    -   to transmit a beacon signal to the one or more other in-coverage        communications devices which can act as a relay node for the        communications device when out-of-coverage, and    -   to transmit the signals representing the data to one of the        other in-coverage communications devices to act as a target        relay node for transmitting the data to the infrastructure        equipment, or    -   to receive the signals representing the data from one of the        other in-coverage communications devices acting as a target        relay node which have been received from the infrastructure        equipment.

Paragraph 2. A communications device according to paragraph 1, whereinthe controller is configured with the transmitter and the receiver

-   -   to transmit signals representing the data to a first in-coverage        communications device acting as source relay node for the        communications device, the first in-coverage communications        device being able to transmit signals to the infrastructure        equipment of the mobile communications network, and    -   to receive signals representing the data from the first        in-coverage communications device acting as the source relay        node, the source relay node being within a coverage area of the        infrastructure equipment of the mobile communications network,        the source relay node being configured to transmit the signals        representing the data received from the communications device to        the infrastructure equipment and to transmit the signals        representing the data to the communications device which are        received from the infrastructure equipment.

Paragraph 3. A communications device according to paragraph 1 or 2,wherein the controller is configured

-   -   to compare the received one of beacon signals, and    -   to select one of the in-coverage communications devices to act        as a target relay node.

Paragraph 4. A communications device according to paragraph 3, whereinthe controller is configured in combination with the transmitter totransmit an indication to the in-coverage communications device actingas the relay node for communicating to the infrastructure equipment ofthe selected one of the in-coverage communications devices to act as thetarget relay node.

Paragraph 5. A communications device according to paragraph 4, whereinthe controller is configured in combination with the transmitter totransmit the indication of the selected one of the in-coveragecommunications devices to act as the target relay node to the selectedone of the in-coverage communications devices for transmission by theselected one of the in-coverage communications devices to theinfrastructure equipment.

Paragraph 6. A communications device according to paragraph 4, whereinthe controller is configured in combination with the transmitter totransmit the indication of the selected one of the in-coveragecommunications devices to act as the target relay node to the first ofthe in-coverage communications devices for transmission by the first ofthe in-coverage communications devices to the infrastructure equipment.

Paragraph 7. A communications device according to paragraph or 2,wherein the controller is configured in combination with the transmitter

-   -   to transmit a relative strength of the beacon signals received        from the one or more other in-coverage communications devices        which can act as relay nodes to the infrastructure equipment via        the first in-coverage communications device acting as the source        relay node, and    -   to receive from the infrastructure equipment via the first        in-coverage communications device acting as the source relay        node an indication of one of the other in-coverage        communications devices which should act for the communications        device as a target relay node.

Paragraph 8. A communications device according to any of paragraphs 1 to7, wherein the predetermined conditions include a quality ofcommunicating the data received from or transmitted to the firstin-coverage communications device.

Paragraph 9. A communications device according to any of paragraphs 1 to7, wherein the predetermined conditions include a signal strength of asignal received from the first of the in-coverage communications devicefalling below a predetermined threshold.

Paragraph 10. A communications device, comprising

-   -   a transmitter configured to transmit signals to one or more        other communications devices via a wireless access interface to        perform device-to-device communications and to transmit signals        via the wireless access interface to an infrastructure equipment        of a mobile communications network when within a radio coverage        area of the infrastructure equipment,    -   a receiver configured to receive signals from the one or more        other communications devices via the wireless access interface        and to receive signals via the wireless access interface from        the infrastructure equipment of the mobile communications        network when within the radio coverage area of the        infrastructure equipment, and    -   a controller for controlling the transmitter and the receiver to        transmit or to receive the signals via the wireless access        interface to transmit or to receive data represented by the        signals, and the transmitter and the receiver are configured        with the controller    -   to receive an indication that the communications device is an        in-coverage communications device to act as a target relay node        for an out-of-coverage communications device,    -   to receive signals representing up-link data from an        out-of-coverage communications device in accordance with a        device to device communications for the infrastructure equipment        of the mobile communications network, and    -   to transmit signals representing the up-link data to        infrastructure equipment, or    -   to receive signals representing down-link data from the        infrastructure equipment, and    -   to transmit signals representing the down-link data to the        out-of-coverage communications device in accordance with a        device to device communications.

Paragraph 11. A communications device according to paragraph 10, whereinthe indication that the communications device is an in-coveragecommunications device to act as a relay node for the out-of-coveragecommunications device comprises receiving up-link data from theout-of-coverage communications device, the out-of-coveragecommunications device having selected the communications device as atarget relay node.

Paragraph 12. A communications device according to paragraph 10, whereinthe indication that the communications device is an in-coveragecommunications device to act as a relay node for the out-of-coveragecommunications device comprises receiving the indication from theinfrastructure equipment.

Paragraph 13. A communications device according to paragraph 10, 11 or12, wherein controller in combination with the transmitter and thereceiver is configured

-   -   to receive a beacon signal transmitted by the out-of-coverage        communications device,    -   to determine a signal strength of the received beacon signal,        and    -   to transmit an indication of the signal strength of the received        beacon signal to one of the out-of-coverage communications        device or the infrastructure equipment.

Paragraph 14. A communications device according to paragraph 10, 11 or12, wherein controller in combination with the transmitter and thereceiver is configured

-   -   to receive a request to transmit a beacon signal from the        out-of-coverage communications device,    -   to transmit the beacon signal to the out-of coverage        communications device in accordance with a device to device        communications protocol, the communications device being        selected to act as the target relay node for an out-of-coverage        communications device by the out-of-coverage communications        device or the infrastructure equipment in accordance with the        beacon signal received by the out-of-coverage communications        device.

Paragraph 15. A communications device, comprising

-   -   a transmitter configured to transmit signals to one or more        other communications devices via a wireless access interface to        perform device-to-device communications and to transmit signals        via the wireless access interface to an infrastructure equipment        of a mobile communications network when within a radio coverage        area of the infrastructure equipment,    -   a receiver configured to receive signals from the one or more        other communications devices via the wireless access interface        and to receive signals via the wireless access interface from        the infrastructure equipment of the mobile communications        network when within the radio coverage area of the        infrastructure equipment, and    -   a controller for controlling the transmitter and the receiver to        transmit or to receive the signals via the wireless access        interface to transmit or to receive data represented by the        signals, and the transmitter and the receiver are configured        with the controller    -   to receive signals representing up-link data from an        out-of-coverage communications device in accordance with a        device to device communications for the infrastructure equipment        of the mobile communications network, and    -   to transmit signals representing the up-link data to        infrastructure equipment, or    -   to receive signals representing down-link data from the        infrastructure equipment, and

to transmit signals representing the down-link data to theout-of-coverage communications device in accordance with a device todevice communications to act as a source relay to the out-of-coveragecommunications device,

-   -   subject to predetermined conditions, to transmit a request to        one or more other in-coverage communications devices or the        infrastructure equipment to transmit a beacon signal to the        out-of-coverage communications device, so that, based upon a        signal quality of the beacon signal received from the one or        more other in-coverage communications devices, one of the one or        more other in-coverage communications devices can be selected to        act as a target relay for the out-of-coverage communications        device.

Paragraph 16. A communications device according to paragraph 15, whereinthe predetermined conditions include a signal quality of one or moresignals received by the receiver or an indication of a signal quality,received by the receiver of a signal transmitted by the transmitter andreceived by the out-of-coverage communications device, falling below apredetermined threshold.

Paragraph 17. A communications device according to paragraph 15 or 16,wherein the controller is configured in combination with the transmitterand the receiver

-   -   to receive an indication, from the out-of-coverage        communications device of a received signal strength of the        beacon signal, received by the out-of-coverage communications        device from each of the one or more other in-coverage        communications devices, and    -   to transmit each of the indications of the received signal        strength of the beacon signal to the infrastructure equipment to        select one of the one or more in-coverage communications devices        to act as a target relay node.

REFERENCES

-   [1] LTE for UMTS: OFDMA and SC-FDMA Based Radio Access, Harris Holma    and Antti Toskala, Wiley 2009, ISBN 978-0-470-99401-6.-   [2] “LTE Device to Device Proximity Services—Radio Aspects”    described in RP-122009.-   [3] 3GPP technical report 36,843.-   [4] ftp://ftp.3gpp.org/tsg_ran/TSG_RAN/TSGR_66/Docs/RP-142229.zip-   [5] EP14184600.6-   [6] PCT/2014/078087-   [7] PCT/2014/078093-   [8] PCT/2014/079338-   [9] PCT/2014/077447-   [10] PCT/2014/077396-   [11] PCT/2014/079335

What is claimed is:
 1. A communications device, comprising: atransmitter configured to transmit signals to one or more othercommunications devices via a wireless access interface to performdevice-to-device (D2D) communications, the wireless access interfacebeing provided for transmitting signals to an infrastructure equipmentof a mobile communications network when within a radio coverage area ofthe infrastructure equipment; a receiver configured to receive signalsfrom the one or more other communications devices via the wirelessaccess interface, the wireless access interface being provided forreceiving signals from the infrastructure equipment of the mobilecommunications network when within the radio coverage area of theinfrastructure equipment; and a controller configured to control thetransmitter and the receiver to transmit or to receive the signals viathe wireless access interface to transmit or to receive data representedby the signals, wherein in a case that predetermined conditions are met,the controller is configured in combination with the transmitter and thereceiver to when the communications device is out-of-coverage so thatthe communications device cannot receive the signals from theinfrastructure equipment or the communications device cannot transmitthe signals to the infrastructure equipment, receive one or more beaconsignals from one or more other in-coverage communications devices whichact as a relay node for the communications device or transmit a beaconsignal to the one or more other in-coverage communications devices,transmit the signals, representing the data, to one of the otherin-coverage communications devices to act as a target relay node fortransmitting the data to the infrastructure equipment, or receive thesignals from one of the other in-coverage communications devices actingas the target relay node which have been received from theinfrastructure equipment, and when the communications device isin-coverage so that the communications device can receive the signalsfrom the infrastructure equipment or the communications device cantransmit the signals to the infrastructure equipment, receive a request,to transmit a beacon signal, from an out-of-coverage communicationsdevice, and transmit the beacon signal to the out-of-coveragecommunications device in accordance with a D2D communications protocol,the communications device being selected to act as the target relay nodefor the out-of-coverage communications device by the out-of-coveragecommunications device or the infrastructure equipment in accordance withthe beacon signal received by the out-of-coverage communications device.2. The communications device as claimed in claim 1, wherein thecontroller is configured in combination with the transmitter and thereceiver to transmit signals representing the data to a firstin-coverage communications device acting as source relay node for thecommunications device, the first in-coverage communications device beingable to transmit signals to the infrastructure equipment of the mobilecommunications network, and receive signals representing the data fromthe first in-coverage communications device acting as the source relaynode, the source relay node being within a coverage area of theinfrastructure equipment of the mobile communications network, thesource relay node being configured to transmit the signals representingthe data received from the communications device to the infrastructureequipment and to transmit the signals representing the data to thecommunications device which are received from the infrastructureequipment.
 3. The communications device as claimed in claim 1, whereinthe controller is configured to compare the received one or more beaconsignals, and select one of the in-coverage communications devices to actas the target relay node.
 4. The communications device as claimed inclaim 3, wherein the controller is configured in combination with thetransmitter to transmit an indication to the in-coverage communicationsdevice acting as the relay node for communicating to the infrastructureequipment of the selected one of the in-coverage communications devicesto act as the target relay node.
 5. The communications device as claimedin claim 4, wherein the controller is configured in combination with thetransmitter to transmit the indication of the selected one of thein-coverage communications devices to act as the target relay node tothe selected one of the in-coverage communications devices fortransmission by the selected one of the in-coverage communicationsdevices to the infrastructure equipment.
 6. The communications device asclaimed in claim 4, wherein the controller is configured in combinationwith the transmitter to transmit the indication of the selected one ofthe in-coverage communications devices to act as the target relay nodeto the first of the in-coverage communications devices for transmissionby the first of the in-coverage communications devices to theinfrastructure equipment.
 7. The communications device as claimed inclaim 1, wherein the controller is configured in combination with thetransmitter and the receiver to transmit a relative strength of thebeacon signals received from the one or more other in-coveragecommunications devices which can act as relay nodes to theinfrastructure equipment via the first in-coverage communications deviceacting as the source relay node, and receive from the infrastructureequipment via the first in-coverage communications device acting as thesource relay node an indication of one of the other in-coveragecommunications devices which should act for the communications device asthe target relay node.
 8. The communications device as claimed in claim1, wherein the predetermined conditions include a quality ofcommunicating the data received from or transmitted to the firstin-coverage communications device.
 9. The communications device asclaimed in claim 1, wherein the predetermined conditions include asignal strength of a signal received from the first of the in-coveragecommunications device falling below a predetermined threshold.
 10. Acommunications device, comprising: a transmitter configured to transmitsignals to one or more other communications devices via a wirelessaccess interface to perform device-to-device (D2D) communications, andtransmit signals via the wireless access interface to an infrastructureequipment of a mobile communications network when within a radiocoverage area of the infrastructure equipment; a receiver configured toreceive signals from the one or more other communications devices viathe wireless access interface, and receive signals via the wirelessaccess interface from the infrastructure equipment of the mobilecommunications network when within the radio coverage area of theinfrastructure equipment; and a controller configured to control thetransmitter and the receiver to transmit or to receive the signals viathe wireless access interface to transmit or to receive data representedby the signals, wherein the controller is configured in combination withthe transmitter and the receiver to receive an indication that thecommunications device is an in-coverage communications device to act asa target relay node for an out-of-coverage communications device,receive signals representing up-link data from the out-of-coveragecommunications device in accordance with D2D communications for theinfrastructure equipment of the mobile communications network, transmitsignals representing the up-link data to infrastructure equipment, orreceive signals representing down-link data from the infrastructureequipment, transmit signals representing the down-link data to theout-of-coverage communications device in accordance with the D2Dcommunications receive a request, to transmit a beacon signal, from theout-of-coverage communications device, and transmit the beacon signal tothe out-of-coverage communications device in accordance with a D2Dcommunications protocol, the communications device being selected to actas the target relay node for an out-of-coverage communications device bythe out-of-coverage communications device or the infrastructureequipment in accordance with the beacon signal received by theout-of-coverage communications device.
 11. The communications device asclaimed in claim 10, wherein the indication that the communicationsdevice is an in-coverage communications device to act as a relay nodefor the out-of-coverage communications device comprises receivingup-link data from the out-of-coverage communications device, theout-of-coverage communications device having selected the communicationsdevice as the target relay node.
 12. The communications device asclaimed in claim 10, wherein the indication that the communicationsdevice is an in-coverage communications device to act as a relay nodefor the out-of-coverage communications device comprises receiving theindication from the infrastructure equipment.
 13. The communicationsdevice as claimed in claim 10, wherein controller in combination withthe transmitter and the receiver is configured to receive a beaconsignal transmitted by the out-of-coverage communications device,determine a signal strength of the received beacon signal, and transmitan indication of the signal strength of the received beacon signal toone of the out-of-coverage communications device or the infrastructureequipment.
 14. A communications device, comprising: a transmitterconfigured to transmit signals to one or more other communicationsdevices via a wireless access interface to perform device-to-device(D2D) communications, and transmit signals via the wireless accessinterface to an infrastructure equipment of a mobile communicationsnetwork when within a radio coverage area of the infrastructureequipment; a receiver configured to receive signals from the one or moreother communications devices via the wireless access interface, andreceive signals via the wireless access interface from theinfrastructure equipment of the mobile communications network whenwithin the radio coverage area of the infrastructure equipment; and acontroller configured to control the transmitter and the receiver totransmit or to receive the signals via the wireless access interface totransmit or to receive data represented by the signals, wherein thecontroller is configured in combination with the transmitter and thereceiver to receive signals representing up-link data from anout-of-coverage communications device in accordance with D2Dcommunications for the infrastructure equipment of the mobilecommunications network, transmit signals representing the up-link datato infrastructure equipment, or receive signals representing down-linkdata from the infrastructure equipment, and transmit signalsrepresenting the down-link data to the out-of-coverage communicationsdevice in accordance with D2D communications to act as a source relay tothe out-of-coverage communications device, in a case that predeterminedconditions are met, transmit a request to one or more other in-coveragecommunications devices or the infrastructure equipment to transmit abeacon signal to the out-of-coverage communications device so that,based upon a signal quality of the beacon signal received from the oneor more other in-coverage communications devices, one of the one or moreother in-coverage communications devices can be selected to act as atarget relay for the out-of-coverage communications device, and in acase that other predetermined conditions are met, receive a request totransmit a beacon signal, from an out-of-coverage communications device,and transmit the beacon signal to the out-of-coverage communicationsdevice in accordance with a D2D communications protocol, thecommunications device being selected to act as the target relay node forthe out-of-coverage communications device by the out-of-coveragecommunications device or the infrastructure equipment in accordance withthe beacon signal received by the out-of-coverage communications device.15. The communications device as claimed in claim 14, wherein thepredetermined conditions include a signal quality of one or more signalsreceived by the receiver or an indication of a signal quality, receivedby the receiver of a signal transmitted by the transmitter and receivedby the out-of-coverage communications device, falling below apredetermined threshold.
 16. The communications device as claimed inclaim 14, wherein the controller is configured in combination with thetransmitter and the receiver to receive an indication, from theout-of-coverage communications device of a received signal strength ofthe beacon signal, received by the out-of-coverage communications devicefrom each of the one or more other in-coverage communications devices,and transmit each of the indications of the received signal strength ofthe beacon signal to the infrastructure equipment to select one of theone or more in-coverage communications devices to act as a target relaynode.
 17. A method of transmitting data from a communications device toan infrastructure equipment of a mobile communications network orreceiving data from an infrastructure equipment by a communicationsdevice, the method comprising: subject to predetermined conditions, whenthe communications device is out-of-coverage so that the communicationsdevice cannot receive signals representing data from the infrastructureequipment or the communications device cannot transmit the signals tothe infrastructure equipment, receiving one or more beacon signals fromone or more in-coverage communications devices which act as a relay nodefor the communications device, or transmitting a beacon signal to theone or more other in-coverage communications devices; transmitting thesignals, representing the data, to one of the other in-coveragecommunications devices to act as a target relay node for transmittingthe data to the infrastructure equipment, or receiving the signals fromone of the other in-coverage communications devices acting as the targetrelay node which have been received from the infrastructure equipment;and when the communications device is in-coverage so that thecommunications device can receive the signals from the infrastructureequipment or the communications device can transmit the signals to theinfrastructure equipment, receiving a request, to transmit a beaconsignal, from an out-of-coverage communications device; and transmittingthe beacon signal to the out-of-coverage communications device inaccordance with a D2D communications protocol, the communications devicebeing selected to act as the target relay node for the out-of-coveragecommunications device by the out-of-coverage communications device orthe infrastructure equipment in accordance with the beacon signalreceived by the out-of-coverage communications device.
 18. The method asclaimed in claim 17, the method further comprising: transmitting thesignals representing the data to a first in-coverage communicationsdevice acting as source relay node for the communications device, thefirst in-coverage communications device being able to transmit signalsto the infrastructure equipment of the mobile communications network; orreceiving the signals representing the data from the first in-coveragecommunications device acting as the source relay node, the source relaynode being within a coverage area of the infrastructure equipment of themobile communications network, the source relay node being configured totransmit the signals representing the data received from thecommunications device to the infrastructure equipment and to transmitthe signals representing the data to the communications device which arereceived from the infrastructure equipment.